The present invention relates to modular jack structures, and more particularly, to an improved structure in the insertion legs of modular jacks.
Modular jacks are connecting devices used widely in telephones, fax machines, modems, portable computers for fast and convenience connections. They play an important role in information system integration and are indispensable components usually seen on circuit boards.
In assembly, however, the process of mounting modular jacks on circuit boards is very complicated and laborious. FIG. 1 shows a prior art modular jack A. Its structural body is made of heat-resistant plastics and having a pair of securing legs D on the bottom. The front side is open-spaced for receiving a plug. The rear side B is half-closed and provided with a lineup of grooves for accommodating pin conductors T. The insertion leg D is integrally formed with the structural body and has a split in the middle S. The head H of the insertion leg is tapered in a hook shape such that, when inserted into a hole on the circuit board, it can be fastened to the circuit board. The length d from the head H to the jack structural body is the same as the thickness of the circuit board. Thus, the length l of the pin conductors must be l.gtoreq.h+d. Pin conductors are often made of expensive gold-plated phosphorous bronze, the cost is therefore high. Besides, after being mounted on circuit boards, overly extended part of the pin conductor has to trimmed off, resulting in a waste of material.
Moreover, component-mounted circuit boards have to go through soldering furnaces so as to secure each component to the circuit boards by means of soldering. The melting point for tin is around 250.degree. C. to 280.degree. C. If the prior art modular jack goes through the soldering furnace, its plastic-made insertion leg will be melted. For this reason, the process is divided into two stages. In the first stage, heat-resistant tapes are attached to cover holes 31 and 23 (see FIG. 7) that are used for accommodating insertion legs and pin conductors. After the soldering, these tapes are removed and then the prior art modular jack is mounted on the circuit board. Manual work is required to solder the pin conductors T to the circuit board. After that, overly extended part of the pin conductors are trimmed off.
Although heat-resistance plastics can be used to mold the jack structural body, the split S in the insertion leg may be, however, filled with chunks of tin after undergoing the soldering process. In later applications, these tin chunks may fall off onto the circuit board, causing short-circuit. Accordingly, using heat-resistant plastics still requires the attachment of tapes and does nothing good to the simplifying of the process.
Since the insertion leg in the prior art modular jack is provided with a tapered and hook-shaped head, its length is as long as 3.1-3.5 mm. This makes the length of the pin conductors larger than 4 mm, which is much greater than standard thickness (1.78 mm) of most circuit boards. This overly extended length, after the process, must be trimmed off, resulting in waste of material.
The length d from the head of the insertion leg to the bottom of the jack structural body is often fixed. However, circuit boards are often with various thicknesses, including 1.0 mm, 1.6 mm, 1.78 mm, 2.0 mm, and so on. If d is 2.0 mm, it would cause instability in the mounting of the jack. When plugs are repeatedly coupled and decoupled, the soldered connection between pin conductors and the circuit board may be subject easily to detachment. This would cause interference or interruption in the signal transmitted through the modular jack, and thus unreliability of the whole system.
In the final stage, tin-plated circuit boards must undergo a washing process. In conventional methods, liquid CFC coolant is injected on the assemblage to remove rosin oil and other chemical substances. After the ban on the use of CFC in 1993, water is used in substitute. It can be seen from FIG.1 that after the water washing process, water may stay inside the prior art modular jack. Jet gun must thus be used to remove the residual water. This add a further step in the assembling process and thus increase the cost.